The hydronephrosis and hydroureter resulting from extrinsic compression of the ureter by pelvic tumor may be considerable when the obstruction causes sufficient back pressure. Slight to moderate block is followed by correspondingly less pronounced changes. It is known that relief of such obstruction results in recession of the dilatation of the collecting system. Kretschmer and Kanter (6), Everett and Sturgis (4), Braasch and Emmett (1), Lich (7), Gartman (5), Robinson (8), and Conger and Toub (2), obtained intravenous urograms showing return to normal after operation for relief of hydronephrosis secondary to extrinsic or intrinsic ureteral blockage. Most of their examinations had been performed from two months to ten years after operation in an effort to assay the results of surgical intervention rather than to estimate the speed of return to radiographic normalcy. In the study to be reported here the question as to how soon relief occurs after operation was investigated by a comparison of preoperative intravenous urograms with those made within six to twenty-six days after operation, in 7 patients with unilateral or bilateral hydronephrosis. The ureteral compression was produced by fibroids in 4 patients, para-ovarian cysts in 1, ovarian cysts in 1, and a tubo-ovarian abscess in the seventh. Case Reports Case I A. S., a 41-year-old white female, was admitted because of gradually increasing menorrhagia for three years and visibly increased abdominal girth for six months. The past medical history was not remarkable. Abdominal examination revealed a mass extending to one fingerbreadth below the umbilicus. On pelvic examination an asymmetrical, nontender, mobile, multilobular uterus the size of a four-month gestation was palpated. The patient was normotensive. Laboratory findings at this time were: hemoglobin 7.2 gm. per 100 ml., microhematocrit 28 per cent, white blood count 17,000 with a normal differential count, sedimentation rate 38 mm. in an hour, and urea nitrogen 12 mg. per 100 c.c. Serum Aschheim-Zondek test was negative. Intravenous urography revealed an intrapelvic mass indenting the superior aspect of the bladder. Excretion from the right kidney was delayed. After sixty-five minutes both collecting systems were outlined and showed definite hydronephrotic changes. Barium-enema examination demonstrated displacement of the sigmoid flexure by a predominantly right-sided mass. The possibility of intrinsic blockage by calculi was excluded by ureteral catheterization and retrograde urography. At operation an irregularly enlarged fibroid uterus the size of a twenty-week gestation was removed. The postoperative course was uneventful. Intravenous urography performed six days after operation showed prompt excretion on both sides. The bilateral hydronephrosis previously observed was no longer present. Both renal pelves, their calyces, and both ureters were normal in caliber.